The present invention relates to a semiconductor device, and a method for producing the device, in particular, a technique that can be used suitably for a semiconductor device having a high-breakdown-voltage transistor.
For example, a MOSFET (metal oxide semiconductor field effect transistor) used in the state that a high voltage of several tens of volts is applied to a drain region thereof is disclosed in Japanese Unexamined Patent Application Publication (JP-A) No. 2008-4649 (Patent Document 1). According to this publication, a buried layer is formed between a semiconductor substrate and a semiconductor layer over the substrate. In order that the buried layer can restrain the action of a parasitic bipolar transistor generated in the vertical direction (in the upper and lower direction), the concentration of a dopant (impurity) in the buried layer, which corresponds to the base of the parasitic transistor, is made sufficiently large.